Food products containing elevated levels of whole grain are recommended by the 2005 dietary guidelines published by the USDA as constituting half of a person's grain consumption, because whole grains are a good source of nutrients of concern. For adults, these nutrients include calcium, potassium, fiber, magnesium, and vitamins A (as carotenoids), C, and E. However, consumption of whole grain foods has lagged mainly due to certain qualities of whole grain foods, such as coarse, gritty appearance and texture from the whole grain flour ingredient typically available for use. More recently, commercial whole grain wheat flours are marketed with reduced particle size; however, these flours exhibit very poor food processing performance in cookies, crackers, breakfast cereals and other baked goods due to fine grinding of the whole grain to particle sizes of less than 150 microns, resulting in starch damage. Furthermore, these fine ground flours have much poorer storage stability than other whole grain wheat flours. Commercial stabilized whole grain wheat flours containing stabilized components such as bran and germ are expected to have better storage stability. However, the functionality of the flours, especially for cookie, cracker and cereal production, for example in terms of dough machinability and cookie spread, is greatly compromised due to significant amounts of gelatinized and damaged starch in the flour.
It is generally known that whole grain wheat flours containing bran and germ are less stable than white refined wheat flours. Storage of whole grain wheat flours for as little as 30 days at 75° F. can result in the development of undesirable odors and flavors in products made with the whole grain flour. Concurrent with the development of off-flavors is an increase in the amount of free fatty acids in the flours, correlated with increased rate of oxygen uptake in the flours and the formation of the oxidative components of rancidity. Decreasing particle size increases the rate and extent of the deterioration of grain components. Heat and moisture treatment is commonly used to inactivate enzymes responsible for flour deterioration, although it is recently shown to contribute to oxidative rancidity as measured by hexanal formation, a common marker used to detect oxidative rancidity, in oat flour. This increase in oxidative rancidity is believed to be due to disintegration of cellular structures that tend to stabilize lipids, or due to inactivation of heat-labile antioxidants.
Rancidity in cereal products may be due to hydrolytic (enzymatic) or oxidative degradation reactions, or both. Often, hydrolysis may predispose products to subsequent oxidative rancidity. Nature has provided a number of protective features in seeds to prevent rancidity and spoilage, enabling seeds to survive periods of adverse conditions before attaining an appropriate environment for germination and growth. Rancidity is less likely to develop when lipid materials, for example, seed oil, are unable to interact with reactants or catalysts such as air and enzymes. One protective feature in cereal grains is the provision of separate compartments for storing lipids and enzymes so that they cannot interact.
Milling cereal grains involves breaking down the separate compartments, bran, germ and endosperm, such that the lipid and enzymatic components of the grain are able to interact, greatly increasing the development of rancidity. Increasing milling to reduce grittiness caused by bran particles tends to increase surface area, reduce natural encapsulation of lipids, and increase interaction between the lipids and enzymatic components thereby increasing the development of rancidity.
Thus, high-extraction flours, that is, those containing substantial amounts of bran and germ, are less stable than white flours. Prolonged storage of high-extraction flours often leads to the development of rancidity. Rancidity includes adverse quality factors arising directly or indirectly from reactions with endogenous lipids, producing a reduction in baking quality of the flour, undesirable tastes and odors, and/or unacceptable functional properties. A main reason for the development of rancidity in high-extraction flours is the enzymatic degradation of unstable natural oils. Rich supplies of unstable natural oils are contained in the germ portion of grains used to make high-extraction flours. White flours, on the other hand, contain little or no unstable natural oils or fats because they are made predominantly from the endosperm portion of grains and are generally substantially free of bran and germ.
Another reason rancidity is a greater problem in products derived from bran and germ-containing flour is that bran and germ contain the enzymes involved in enzyme-catalyzed lipid degradation. One of the enzymes, lipase, causes hydrolytic rancidity in milled products of sound, ungerminated wheat. Lipase is found almost exclusively in the bran component. The other key lipid-degrading enzyme, lipoxygenase (LPO), is present almost exclusively in the germ and also is involved in the development of rancidity. Thus, bran-containing wheat flours or graham flours are much more susceptible to the development of rancidity than are white flours which contain little or no bran and germ.
Enzyme-catalyzed lipid degradation that occurs in high extraction wheat flour, causing rancidity in such flour, is believed to occur by the action of lipase followed by the action of LPO. When lipase, the enzyme found almost exclusively in the bran portion of the grain, is activated during milling, it reacts with unstable oils naturally occurring in the grain and breaks down the unstable oils to free fatty acids (FFA). This process may take weeks or even months. Then, LPO, the enzyme found almost exclusively in the germ portion of the grain, oxidizes FFA in the presence of oxygen, producing volatile breakdown products such as peroxides that, in turn, generate rancid aldehydes. In the absence of moisture, oxidation of FFA is also a very slow process and can take up to several weeks until noticeable amounts of rancid aldehydes can be detected. However, in the presence of moisture, or water, that is normally added to wheat flour in large amounts during the dough work-up stage, enzyme-catalyzed oxidation of free fatty acids tends to proceed to a great extent very quickly, causing formation of large amounts of rancid aldehydes in a matter of just a few minutes.
U.S. Patent Application Publication No. US 2005/0136173 A1, to Korolchuk, discloses a process of producing an ultrafine-milled whole-grain wheat flour and the products thereof. Ultrafine is defined as having a particle size of less than or equal to about 150 microns. The process is a continuous flow-grain-milling process, including the steps of separating a quantity of cleaned and tempered wheat kernels into a fine fraction, comprised primarily of endosperm along with small amounts of residual bran and germ, and a coarse fraction, comprised of bran, germ, and a small amount of residual endosperm. The coarse fraction is ground through a mill, such as a gap mill, to form an ultrafine-milled coarse fraction having a particle size of less than or equal to about 150 micron. Finally, the ultrafine-milled coarse fraction is mixed with the fine fraction in order to form the ultrafine-milled whole-grain wheat flour. In the Korolchuk process, the two fractions are milled to produce fractions and an ultrafine-milled whole-grain wheat flour having particle sizes less than or equal to about 150 microns. According to Korolchuk, the flour has the full nutritional value of wheat kernels, while retaining the texture of refined wheat flour and an appearance similar to refined wheat flour, and thus, the flour can be used in food products such as bakery products and snack food products, which typically use refined wheat flour. However, production of a coarse fraction with very little residual endosperm generally requires increased milling and grinding operations which can damage the starch and adversely affect dough machinability and cookie production. Also, grinding of the coarse fraction to a particle size of less than or equal to about 150 microns causes increased interaction between the lipids and lipid-degrading enzymes, which results in increased rancidity problems.
U.S. Patent Application Publication No. US 2006/0073258 A1, to Korolchuk, discloses the production of an ultrafine-milled whole-grain wheat flour which has the full nutritional value of wheat kernels, while retaining the texture of refined wheat flour and an appearance similar to refined wheat flour. Production of an ultrafine-milled coarse fraction which can be used as a replacement and to fortify refined wheat flour is also disclosed. An objective of the Korolchuk process is to obtain an ultrafine-milled whole grain wheat flour that has a particle size distribution that meets the FDA standards for a refined wheat flour product of a particle size in which not less than 98% passes through a U.S. Wire 70 sieve (210 microns). In the Korolchuk process, an ultrafine-milled fine fraction comprising endosperm and a coarse fraction comprising bran and germ are obtained. The coarse fraction is ground in a gap mill to reduce microbial load, and the ultrafine-milled coarse fraction is then mixed with the ultrafine-milled fine fraction to obtain an ultrafine-milled whole-grain wheat flour. According to Korolchuk, grinding the coarse fraction in a gap mill to a particle size less than or equal to 500 microns reduces the microbial load. After sifting, any ground coarse fraction having a particle size greater than 500 microns is returned to the process for further milling. Stabilization of a bran component or whole wheat flour by heating a coarse fraction comprising bran and germ to inactivate lipase is not disclosed.
Japanese Patent Publication No. JP 205168451 A discloses that a wheat flour having a mean particle diameter of 150 to 230 microns and an ash content of 0.8 to 1.2% does not have a grassy-smelling wheat bran smell, is rich in nutritive value and flavor, and can be used in the production of noodles, and confectionery. Heat-treatment of the flour to inactivate enzymes such as lipase and lipoxygenase is not disclosed.
Use of steam or other heat sources to inactivate enzymes such as lipase and lipoxygenase in whole grains is disclosed in U.S. Pat. No. 4,737,371 to Bookwalter, U.S. Pat. No. 5,066,506 to Creighton et al, and U.S. Pat. No. 6,616,957 to Wilhelm et al. However, treatment of the whole grain generally requires an increased amount of cooling and drying of the treated whole grains to reduce their moisture content to microbially shelf-stable levels. Also, steam heat treatment, such as employed in U.S. Pat. No. 4,737,371 to Bookwalter tends to substantially gelatinize starch in the berries or fails to substantially completely inactivate lipase and LPO.
In Bookwalter, U.S. Pat. No. 4,737,371, steam treatment for a 4-12 minute period of time only “significantly reduces” lipase activity but does not substantially inactivate lipase. When steam-treating under conditions sufficient to substantially inactivate lipase and LPO, steam penetrates the berries and gelatinizes a substantial amount of starch in the interior endosperm of the berries. The moisture from steam induces gelatinization of starch in the berries, when combined with the heat brought to the interior of the berries by the steam. The excessive moisture which penetrates the berries during steaming also necessitates long drying periods to reduce the moisture content to an acceptable level for milling.
In one embodiment, U.S. Pat. No. 4,737,371 to Bookwalter discloses that, in the case of large-grained cereals and those which are otherwise easily degerminated, such as corn and wheat, it would be advantageous to first mill the grain and then treat only the separated germ with steam, so that equipment and processing costs would be held to a minimum. Thereafter, it is disclosed, the germ can be recombined with the endosperm. The term “whole” as used by Bookwalter means that both the endosperm and germ are present, though the hull, husk, and bran layers may have been previously removed. However, the combined product, even though it is called a whole-grain product, does not contain bran in the natural proportions present in the original whole grain.
In U.S. Pat. No. 5,066,506 to Creighton et al, a short time (30 seconds to 60 seconds), high temperature (400° F. to 650° F.) and high pressure (50 psig to 70 psig) treatment of the whole grain kernel is employed to inactivate the enzymes involved in rancidity development. Gelatinization of starch can be as high as 40% of the total starch in the kernel, which can decrease dough machinability and cookie spread. Also, the high temperatures and pressures employed would tend to increase acrylamide production and vitamin destruction.
In U.S. Pat. No. 6,616,957 to Wilhelm et al, whole wheat berries having a moisture content of from about 15% by weight to about 20% by weight are irradiated with infrared (IR) energy, the berries are optionally maintained at an elevated temperature of from about 80° C. to about 110° C. for a period of time up to about one hour, and the treated berries are cooled, dried and comminuted. The moisture content of the berries can be adjusted by moistening or tempering the berries prior to treatment with IR energy. The moisture content, optional tempering conditions, amount of irradiated IR energy, the elevated temperature, and the various treatment periods are sufficient to inactivate lipase and lipoxygenase in the berries, yet insufficient to gelatinize more than about 20% of the starch in the berries.
Whole grain wheat flours having a high degree of starch damage and/or a high degree of gelatinization may be acceptable for ready-to-eat breakfast cereals or other applications where crunchiness is desired, but dough formation, sheeting, or cutting or oven spread during baking is not a concern. The present invention provides a process for making stabilized whole grain wheat flours containing natural proportions of bran, germ, and endosperm, with low degrees of starch damage due to abrasion and low degrees of starch gelatinization due to heat and moisture treatment. The stabilized whole wheat flours of the present invention have dough and baking functionalities approaching those of white refined wheat flour. They may be used in the consistent production of highly machinable, sheetable doughs for making baked goods such as cookies, crackers, and snacks with excellent oven spread and appearance, and a non-gritty mouthfeel.
The present invention provides stabilized whole grain wheat flour and a stabilized bran component which exhibit unexpectedly low sodium carbonate-water sorption, and an unexpectedly long shelf life, with unexpectedly low free fatty acid contents and hexanal contents at 1 month or more under accelerated storage conditions. A high level of enzyme inactivation is achieved, while retaining unexpectedly high levels of essential nutrients, such as antioxidants and vitamins that are lost with high temperature stabilization treatments. Furthermore, acrylamide formation is controlled to unexpectedly low levels using the stabilization conditions of the present invention.
The present invention also provides a method of whole wheat berry or whole grain stabilization which meets the standard of identity for ingredient labeling proposed by the FDA and AACCI for identifying the ingredient as “whole grain”. As indicated in the U.S. Food and Drug Administration Feb. 15, 2006 draft guidance and as used herein, the term “whole grain” includes cereal grains that consist of the intact, ground, cracked or flaked fruit of the grains whose principal components—the starchy endosperm, germ and bran—are present in the same relative proportions as they exist in the intact grain. This definition is nearly the same as AACC International's definition of “Whole grains shall consist of the intact, ground, cracked or flaked caryopsis, whose principal anatomical components—the starchy endosperm, germ and bran—are present in the same relative proportions as they exist in the intact caryopsis” which was approved in 1999 and is applicable herein. The FDA outlined that such grains may include barley, buckwheat, bulgur, corn, millet, rice, rye, oats, sorghum, wheat and wild rice. Although this invention is primarily exemplified by reference to wheat berries, as well as corn, rice, and oats, it will be appreciated that other cereal grains are also contemplated to be within the scope of various or certain aspects of the invention. Examples of other whole grains that may be processed in accordance with various or certain embodiments of this invention include, for example, wild rice, rye, barley, buckwheat, bulgar, millet, sorghum, and the like.